I'm making a combustion howitzer that has a 3 inch PVC barrel that is 6 feet long as the barrel, I know that I need a 1.5:1 ratio combustion chamber, but my main concern is heat. Will my Spud gun melt on the inside from this enormous combustion? I also need to know if there are any tips for building these large cannons, such as sparker placement or reinforcing certain parts.Thank you so much for your help, I will post pictures when it is completed.